User interface for identifying midlines of spinal cord

ABSTRACT

Techniques for delivery of electrical neurostimulation therapy to a patient are disclosed. In one example, a processor controls delivery of electrical neurostimulation therapy to a patient by an electrical neurostimulation therapy device and via a plurality of combinations of a plurality of electrodes disposed along a lead inserted across an anatomical midline of a spinal cord of the patient and angled relative to the anatomical midline, the lead connected to the electrical neurostimulation therapy device. The processor determines, based on the electrical neurostimulation therapy, a location of a physiological midline of the spinal cord. The processor selects, based on the location of the physiological midline, at least one electrode of the plurality of electrodes for subsequent delivery of electrical neurostimulation therapy to the patient. Further, the processor displays a representation of the physiological midline and the anatomical midline relative to the spinal cord.

This application is a continuation of U.S. patent application Ser. No.15/639,126, which was filed on Jun. 30, 2017, and is entitled, “USERINTERFACE FOR IDENTIFYING MIDLINES OF SPINAL CORD.” The entire contentof U.S. patent application Ser. No. 15/639,126 is incorporated herein byreference.

TECHNICAL FIELD

This disclosure generally relates to systems for electricalneurostimulation of a patient.

BACKGROUND

Electrical neurostimulation therapy, e.g., for pain relief, may bedelivered by one or more electrodes positioned along one or more leadsinserted into a patient. Positioning of the leads is important toeffectively deliver therapy to target site of the patient. Ideally, inthe case of spinal cord stimulation (SCS) for pain relief, the leadsshould be placed on either side of a physiological midline of a spinalcord of the patient (e.g., a conceptual midline wherein electricalneurostimulation delivered to the left of the physiological midlineprovides pain relief to only a left side of the body of the patient,while electrical neurostimulation delivered to the right of thephysiological midline provides pain relief to only a right side of thebody of the patient). Typically, a physician uses a fluoroscope to placea first lead parallel and left of an anatomical midline of the spinalcord (e.g., a line bisecting the spinal cord into two lateral sections)and a second lead parallel and right of the anatomical midline of thespinal cord. However, the physiological midline only roughly correlatesto the anatomical midline of the spinal cord, and may differ by severalmillimeters. After implanting the leads, the clinician, while still inthe operating room, tests various electrodes combinations among the twoleads and the patient provides feedback as to where the patient feelsparesthesia or reduction of pain. This process is time consuming and maybe inaccurate as the patient suffers disorientation from anesthesia.

SUMMARY

In general, the disclosure describes techniques for more accuratelydelivering electrical neurostimulation to a spinal cord of a patient. Inone example, a clinician implants at least one lead at an angle relativeto and across an anatomical midline of a spinal cord of the patient. Insome examples, the at least one lead is implanted at an angle of 5-20degrees relative to the anatomical midline of the spinal cord. In someexamples of the techniques disclosed herein, the clinician implants afirst and second lead angled 5-20 degrees relative to and across theanatomical midline of the spinal cord. In alternate examples, the firstlead is implanted parallel to and offset from the anatomical midline ofthe spinal cord, while the second lead is implanted at an angle of 5-20degrees relative to and across the anatomical midline of the spinalcord. Such an implantation procedure as described herein may ensure thatat least several electrodes are implanted on either side of thephysiological midline of the spinal cord of the patient.

After surgery, and outside of the operating room, the clinician may testvarious combinations of electrodes to determine the combination thatprovides the greatest pain relief to the patient. The clinician may usefeedback from the patient regarding the different combinations ofelectrodes to identify a position of the physiological midline of thespinal cord of the patient. The clinician may use a user interface tomark, in reference to the first and second leads, the location of theanatomical midline of the spinal cord via a fluoroscope, and to furthermark the location of the physiological midline of the spinal cord viathe patient feedback. Accordingly, such an implantation procedure mayeliminate the need to perform testing of the implanted electrodes withinthe operation room, which may reduce the cost of the procedure, increasethe reliability of the feedback received from the patient, and eliminatethe need to wake the patient up from anesthesia to provide feedback onthe electrical neurostimulation therapy, paresthesia, and painsensations.

In one example, this disclosure describes a method including:controlling, by one or more processors, delivery of electricalneurostimulation therapy to a patient by an electrical neurostimulationtherapy device and via a plurality of combinations of a plurality ofelectrodes, wherein the plurality of electrodes are disposed along alead inserted across an anatomical midline of a spinal cord of thepatient and angled relative to the anatomical midline of the spinalcord, the lead connected to the electrical neurostimulation therapydevice; determining, based on the delivery of the electricalneurostimulation therapy, a location of a physiological midline of thespinal cord of the patient; selecting, based on the location of thephysiological midline of the spinal cord, at least one electrode of theplurality of electrodes for subsequent delivery of electricalneurostimulation therapy to the patient; and controlling, by the one ormore processors, delivery of electrical neurostimulation therapy to thepatient by the electrical neurostimulation therapy device and via theselected at least one electrode of the plurality of electrodes.

In another example, this disclosure describes an electricalneurostimulation therapy system including: a plurality of electrodesdisposed along a lead inserted across an anatomical midline of a spinalcord of a patient and angled relative to the anatomical midline of thespinal cord, the lead connected to an electrical neurostimulationtherapy device; a therapy delivery circuit of the electricalneurostimulation therapy device configured to deliver electricalneurostimulation therapy to the patient via a plurality of combinationsof the plurality of electrodes; and one or more processors configuredto: control delivery of the electrical neurostimulation therapy to thepatient; determine, based on the delivery of the electricalneurostimulation therapy, a location of a physiological midline of thespinal cord of the patient; based on the location of the physiologicalmidline of the spinal cord of the patient, select at least one electrodeof the plurality of electrodes for subsequent delivery of electricalneurostimulation therapy to the patient; and control delivery ofelectrical neurostimulation therapy to the patient by the electricalneurostimulation therapy device and via the selected at least oneelectrode of the plurality of electrodes

In another example, this disclosure describes an electricalneurostimulation therapy system including: a plurality of electrodesdisposed along a lead inserted across an anatomical midline of a spinalcord of a patient and angled relative to the anatomical midline of thespinal cord, the lead connected to an electrical neurostimulationtherapy device; a therapy delivery circuit of the electricalneurostimulation therapy device configured to deliver electricalneurostimulation therapy to the patient via a plurality of combinationsof the plurality of electrodes; and one or more processors configuredto: control delivery of the electrical neurostimulation therapy to thepatient; determine, based on the delivery of the electricalneurostimulation therapy, a location of a physiological midline of thespinal cord of the patient; and present, for display to a user, arepresentation of the spinal cord, the location of the physiologicalmidline of the spinal cord relative to the spinal cord, and a locationof an anatomical midline of the spinal cord relative to the spinal cord.

The details of one or more examples of the techniques of this disclosureare set forth in the accompanying drawings and the description below.Other features, objects, and advantages of the techniques will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example system thatdelivers stimulation therapy to a spinal cord of a patient in accordancewith the techniques of the disclosure.

FIG. 2 is a block diagram illustrating various example components of animplantable electrical stimulator of a system in accordance with thetechniques of the disclosure.

FIG. 3 is a functional block diagram illustrating various components ofan external programmer for an implantable stimulator.

FIGS. 4A-4B are illustrations of example leads for delivering electricalneurostimulation in accordance with the techniques of the disclosure.

FIGS. 5A-5D illustrate an exemplary screen shot of a display on a userinterface of an external programmer, in accordance with the techniquesof the disclosure.

FIG. 6 is a conceptual diagram illustrating a stimulation zone ofelectrical stimulation therapy.

FIG. 7 is a flowchart depicting an example operation according to thetechniques of the disclosure.

Like reference characters refer to like elements throughout the figuresand description.

DETAILED DESCRIPTION

FIG. 1 is a conceptual diagram illustrating system 30 that deliversstimulation therapy to spinal cord 38 of patient 36 in accordance withthe techniques of the disclosure. System 30 delivers electricalneurostimulation therapy from implantable stimulator 34 to spinal cord38 via one or more electrodes (not shown) carried by, i.e., located on,implantable medical leads 32A and 32B (collectively “leads 32”) as wellas the housing of implantable stimulator 34, e.g., housing electrode 37.System 30 and, more particularly, implantable stimulator 34, may operatein in a current-based or voltage-based configuration. That is, in acurrent-based example, implantable stimulator 34 delivers controlledcurrent stimulation pulses or waveforms to patient 36 via one or moreregulated, stimulation electrodes. Alternatively, in a voltage-basedexample, implantable stimulator 34 may be configured to deliver constantvoltage pulses. Various parameters of the pulses or waveforms may bedefined by one or more stimulation programs. The pulses or waveforms maybe delivered substantially continuously or in bursts, segments, orpatterns, and may be delivered alone or in combination with pulses orwaveforms defined by one or more other stimulation programs. In someexample, implantable stimulator 34 delivers spinal cord stimulation(SCS) therapy to patient 36 via the electrodes carried by, i.e., locatedon, leads 32 to provide pain relief therapy to patient 36.

Stimulator 34 may be implanted in patient 36 at a location minimallynoticeable to the patient. For SCS, stimulator 34 may be located in thelower abdomen, lower back, or other location to secure the stimulator.Leads 32 may be tunneled from stimulator 34 through tissue to reach thetarget tissue adjacent to spinal cord 38 for stimulation delivery. Atthe distal ends of leads 32 are one or more electrodes (not shown) thattransfer the stimulation pulses from the lead to the tissuesubstantially simultaneously with stimulation pulses.

In the example of FIG. 1, the distal ends of leads 32 are placedadjacent to the target tissue of spinal cord 38. The proximal ends ofleads 32 may be both electrically and mechanically coupled toimplantable stimulator 34 either directly or indirectly via a leadextension and header. Alternatively, in some examples, leads 32 may beimplanted and coupled to an external stimulator, e.g., through apercutaneous port. In additional example implementations, stimulator 34may be a leadless stimulator with one or more arrays of electrodesarranged on a housing of the stimulator rather than leads that extendfrom the housing.

Application of certain techniques will be described in this disclosurewith respect to implantable stimulator 34 and implantable leads 32having ring electrodes for purposes of illustration. Ring electrodes arecommonly used in electrical neurostimulation applications because theyare simple to program and are capable of delivering an electrical fieldto any tissue adjacent to leads 32. However, other types of electrodesmay be used. For example, the electrodes of leads 32 may have a complexelectrode array geometry that is capable of producing shaped electricalfields. The complex electrode array geometry may include multipleelectrodes (e.g., partial ring or segmented electrodes) around theperimeter of each lead 32, rather than one ring electrode. In thismanner, electrical stimulation may be directed in a specific directionfrom leads 32 to enhance therapy efficacy and reduce possible adverseside effects from stimulating a large volume of tissue. In alternativeexamples, leads 32 may have shapes other than elongated cylinders asshown in FIG. 1. For example, leads 32 may be electrode pads on a paddlelead, circular (i.e., ring) electrodes surrounding the body of leads 32,spherical leads, bendable leads, conformable electrodes, cuffelectrodes, segmented electrodes, or any other type of electrodescapable of forming unipolar, bipolar or multi-polar electrodeconfigurations and effective in treating patient 36. In some examples,one or more of the electrodes may be unregulated. In some examples, thehousing of implantable stimulator 34, e.g., housing electrode 37,functions as an anode and/or return path for the electrical stimulation.

The stimulation pulses may be delivered using various electrodearrangements such as unipolar arrangements, bipolar arrangements ormultipolar arrangements. A unipolar stimulation arrangement generallyrefers to the use of an anode on the housing that sources current andone or more cathodes on one or more leads that sink current. A bipolarstimulation arrangement generally refers to the use of an anode on alead that sources current and a cathode on the same lead and/or anotherlead that sink current. A multipolar stimulation arrangement generallyrefers to the use of more than one anode on a lead that each sourcecurrent and one or more cathodes on the same lead or another lead thatsink current, or the use of one anode on a lead that sources current andmultiple cathodes on the same lead or another lead that sink current. Ahybrid stimulation arrangement that combines both unipolar and bipolarelectrode relationships may be referred to as an omnipolar arrangement.In an omnipolar arrangement, an anode on the housing may be used todeliver stimulation pulses substantially simultaneously with at leastone anode on a lead and at least one cathode on a lead. In this case,for an omnipolar arrangement, at least one anode on a lead and at leastone anode on the housing can be used simultaneously in combination withat least one cathode on a lead. In other omnipolar arrangements, acathode on the housing may be used to deliver stimulation pulsessubstantially simultaneously with at least one cathode on a lead and atleast one anode on a lead. In this alternative case, for an omnipolararrangement, at least one cathode on a lead and at least one cathode onthe housing can be used simultaneously in combination with at least oneanode on a lead. Any of the above electrode arrangements, or otherelectrode arrangements, may be used to deliver electrical stimulation inaccordance with techniques described in this disclosure.

Implantable stimulator 34 delivers stimulation to spinal cord 38 toreduce the amount of pain perceived by patient 36. The stimulationdelivered by implantable stimulator 34 may take the form of stimulationpulses or continuous stimulation waveforms, and may be characterized bycontrolled current or voltage levels, as well as programmed pulse widthsand pulse rates in the case of stimulation current pulses. Stimulationmay be delivered via selected combinations of electrodes located on oneor both of leads 32 and on the housing. Stimulation of spinal cord 38may, for example, prevent pain signals from traveling through the spinalcord and to the brain of the patient. Patient 34 perceives theinterruption of pain signals as a reduction in pain and, therefore,efficacious therapy.

In some examples, therapy system 30 further includes external programmer40. External programmer 40 may be used to define stimulation therapyparameters for use by implantable stimulator 34. In some examples,programmer 40 is a clinician programmer, which is a handheld computingdevice that permits a clinician to program stimulation therapy forpatient 36 via a user interface, e.g., using input keys and a display.For example, using the clinician programmer, the clinician may specifystimulation parameters, i.e., create programs, for use in delivery ofstimulation therapy. The clinician programmer may support telemetry(e.g., radio frequency (RF) telemetry) with implantable stimulator 34 todownload programs and, optionally, upload operational or physiologicaldata stored by implantable stimulator 34. In this manner, the clinicianmay periodically interrogate implantable stimulator 34 to evaluateefficacy and, if necessary, modify the programs or create new programs.In some examples, the clinician programmer transmits programs to apatient programmer (not depicted) in addition to or instead ofimplantable stimulator 34. In some examples, the patient programmer mayserve as the clinician programmer.

In other examples, external programmer 40 is a patient programmer. Likethe clinician programmer, the patient programmer may be a handheldcomputing device. The patient programmer may also include a display andinput keys to allow patient 36 to interact with the patient programmerand implantable stimulator 34. In this manner, the patient programmerprovides patient 36 with a user interface for control of the stimulationtherapy delivered by implantable stimulator 34. For example, patient 36may use the patient programmer to start, stop or adjust electricalstimulation therapy. In particular, the patient programmer may permitpatient 36 to adjust stimulation parameters of a program such asduration, current or voltage amplitude, pulse width and pulse rate.Patient 36 may also select a program, e.g., from among a plurality ofstored programs, as the present program to control delivery ofstimulation by implantable stimulator 34.

With reference to FIG. 1, a user, such as a clinician or patient 36, mayinteract with a user interface of external programmer 40 to programstimulator 34. Programming of stimulator 34 may refer generally to thegeneration and transfer of commands, programs, or other information tocontrol the operation of the stimulator. For example, programmer 40 maytransmit programs, parameter adjustments, program selections, groupselections, or other information to control the operation of stimulator34, e.g., by wireless telemetry. In accordance with this disclosure,programmer 40 may transmit to the stimulator 34 information regardingthe patient and regarding therapy the patient received during previoussessions including, for example, images that show placement of leads 32.

Whether programmer 40 is configured for clinician or patient use,programmer 40 may communicate to implantable stimulator 34 or any othercomputing device via wireless communication. Programmer 40, for example,may communicate via wireless communication with implantable stimulator34 using radio frequency (RF) telemetry techniques known in the art orother communication standards such as, for example, Bluetooth®.Programmer 40 may also communicate with another programmer or computingdevice via a wired or wireless connection using any of a variety oflocal wireless communication techniques, such as RF communicationaccording to the 802.11 or Bluetooth® specification sets, infraredcommunication according to the IRDA specification set, or other standardor proprietary telemetry protocols. Programmer 40 may also communicatewith another programming or computing device via exchange of removablemedia, such as magnetic or optical disks, or memory cards or sticks.Further, programmer 40 may communicate with implantable stimulator 34and other programming devices via remote telemetry techniques known inthe art, communicating via a local area network (LAN), wide area network(WAN), public switched telephone network (PSTN), or cellular telephonenetwork, for example.

Implantable stimulator 34, and external programmer 40 may communicatevia cables or a wireless communication, as shown in FIG. 1. Externalprogrammer 40 may, for example, communicate via wireless communicationwith implantable stimulator 34 using RF telemetry techniques known inthe art or other standard communication protocols such as, for example,Bluetooth®. External programmer 40 also may communicate with each otherusing any of a variety of wireless communication techniques, such as RFcommunication according to the 802.11 or Bluetooth® specification sets,infrared communication, e.g., according to the IrDA standard, or otherstandard or proprietary telemetry protocols. External programmer 40 mayinclude a transceiver to permit bi-directional communication withimplantable stimulator 34.

According to the techniques of the disclosure, a clinician implants atleast one lead 32 at an angle relative to and across an anatomicalmidline of spinal cord 38 of patient 36. In some examples, the at leastone lead 32 is implanted at an angle of 5-20 degrees relative to theanatomical midline of spinal cord 38 of patient 36. In some examples ofthe techniques disclosed herein, the clinician implants a first lead 32Aand second lead 32B angled 5-20 degrees relative to and across theanatomical midline of spinal cord 38. In alternate examples, the firstlead 32A is implanted parallel to and offset from the anatomical midlineof spinal cord 38, while the second lead 32B is implanted at an angle of5-20 degrees relative to and across the anatomical midline of spinalcord 38. Such an implantation procedure as described herein may ensurethat at least several electrodes are implanted on either side of thephysiological midline of spinal cord 38.

After surgical implantation of stimulator 34, and outside of theoperating room, the clinician may test various combinations ofelectrodes to determine the combination that provides the greatest painrelief to the patient. The clinician may use feedback from the patientregarding the different combinations of electrodes to identify aposition of the physiological midline of spinal cord 38. The clinicianmay use a user interface to mark, in reference to the first and secondleads, the location of the anatomical midline of spinal cord 38 via afluoroscope, and to further mark the location of the physiologicalmidline of spinal cord 38 via the patient feedback. Accordingly, such animplantation procedure may eliminate the need to perform testing of theimplanted electrodes within the operation room, which may reduce thecost of the procedure, increase the reliability of the feedback receivedfrom the patient, and eliminate the need to wake the patient up fromanesthesia to provide feedback on the electrical neurostimulationtherapy, paresthesia, and pain sensations.

FIG. 2 is a block diagram illustrating various components of an exampleimplantable stimulator 34 of system 30 in accordance with the techniquesof the disclosure. In the example of FIG. 2, implantable stimulator 34includes processor 50, memory 52, power source 54, telemetry circuitry56, antenna 57, and a stimulation generator 60. Implantable stimulator34 is also shown in FIG. 2 coupled to electrodes 48A-Q (collectively“electrodes 48”). Electrodes 48A-48P are implantable and may be deployedon one or more implantable leads 32. With respect to FIG. 1, lead 32Aand 32B may carry electrodes 48A-H and electrodes 48I-P, respectively.In some cases, one or more additional electrodes may be located on orwithin the housing of implantable stimulator 34, e.g., to provide acommon or ground electrode or a housing anode. With respect to FIG. 2,leads 32A and 32B may carry electrodes 48A-H and electrodes 48I-P,respectively. In the examples of FIGS. 1 and 2, a lead or lead segmentcarries eight electrodes to provide a 2×8 electrode configuration (twoleads with 8 electrodes each), providing a total of sixteen differentelectrodes. The leads may be detachable from a housing associated withimplantable stimulator 34, or be fixed to such a housing.

In other examples, different electrode configurations comprising asingle lead, two leads, three leads, or more may be provided. Inaddition, electrode counts on leads may vary and may be the same ordifferent from a lead to lead. Examples of other configurations includeone lead with eight electrodes (1×8), one lead with 12 electrodes(1×12), one lead with 16 electrodes (1×16), two leads with fourelectrodes each (2×4), three leads with four electrodes each (3×4),three leads with eight electrodes each (3×8), three leads with four,eight, and four electrodes, respectively (4-8-4), two leads with 12 or16 electrodes (2×12, 2×16), two or more leads with 11 or 13 electrodes,or other configurations. Different electrodes are selected to formelectrode combinations. Polarities are assigned to the selectedelectrodes to designate the electrodes as anodes or cathodes and formelectrode configurations.

Electrode 48Q represents one or more electrodes that may be carried on ahousing, i.e., can, of implantable stimulator 34. e.g., housingelectrode 37 of FIG. 1. Electrode 48Q may also be a dedicated short leadextending from the housing, or a proximal portion of one of the leadscarrying electrodes 48A-48P. The proximal portion may be closelyadjacent to the housing, e.g., at or near a point at which a lead iscoupled to the housing, such as adjacent to a lead connection header 8of the housing. Electrode 48Q may be configured as a regulated orunregulated electrode for use in an electrode configuration withselected regulated and/or unregulated electrodes among electrodes48A-48P, which may be located on a lead body of one or more leads, asdescribed above. Electrode 48Q may be formed together on a housing thatcarries the electrode and houses the components of implantablestimulator 34, such as stimulation generator 60, processor 50, memory52, telemetry circuitry 56, and power source 54.

Housing electrode 48Q may be configured for use as an anode to sourcecurrent substantially simultaneously with one or more electrodes 48A-48Pconfigured for use as cathodes sinking current in a unipolararrangement. Housing electrode 48Q may be configured for use as an anodeto source current substantially simultaneously with current sourced byanother electrode 48A-48P configured for use as an anode in an omnipolararrangement. By way of specific example, electrodes 48A, 48B, andhousing electrode 48Q each could be configured for use as anodes.Electrodes 48A, 48B could deliver electrical stimulation currentsubstantially simultaneously with the electrical stimulation currentdelivered via housing electrode 48Q. In this illustration, one or morecathodes could be formed with other electrodes (e.g., any of electrodes48C-48P) on the leads to sink current sourced by anodes 48A, 48B and48Q.

Memory 52 may store instructions for execution by processor 50,stimulation therapy data, sensor data, and/or other informationregarding therapy for patient 36. Processor 50 may control stimulationgenerator 60 to deliver stimulation according to a selected one or moreof a plurality of programs or program groups stored in memory 52. Memory52 may include any electronic data storage media, such as random accessmemory (RAM), read-only memory (ROM), electronically-erasableprogrammable ROM (EEPROM), flash memory, or the like. Memory 52 maystore program instructions that, when executed by processor 50, causethe processor to perform various functions ascribed to processor 50 andimplantable stimulator 34 in this disclosure.

Processor 50 may include one or more microprocessors, digital signalprocessors (DSPs), application-specific integrated circuits (ASICs),field-programmable gate arrays (FPGAs), or other digital logiccircuitry. Processor 50 controls operation of implantable stimulator 34,e.g., controls stimulation generator 60 to deliver stimulation therapyaccording to a selected program or group of programs retrieved frommemory 52. For example, processor 50 may control stimulation generator60 to deliver electrical signals, e.g., as stimulation pulses orcontinuous waveforms, with current amplitudes, pulse widths (ifapplicable), and rates specified by one or more stimulation programs.Processor 50 may also control stimulation generator 60 to selectivelydeliver the stimulation via subsets of electrodes 48, also referred toas electrode combinations, and with polarities specified by one or moreprograms.

Upon selection of a particular program group, processor 50 may controlstimulation generator 60 to deliver stimulation according to theprograms in the groups, e.g., simultaneously or on a time-interleavedbasis. A group may include a single program or multiple programs. Asmentioned previously, each program may specify a set of stimulationparameters, such as amplitude, pulse width and pulse rate, ifapplicable. For a continuous waveform, parameters may include amplitudeand frequency. In addition, each program may specify a particularelectrode combination for delivery of stimulation, and an electrodeconfiguration in terms of the polarities and regulated/unregulatedstatus of the electrodes. The electrode combination may specifyparticular electrodes in a single array or multiple arrays, and on asingle lead or among multiple leads. The electrode combination mayinclude at least one anode on the housing of the IMD, e.g., electrode48Q, at least one anode on a lead, electrode 48A, and at least onecathode on a lead. The lead-borne anode and cathode may be on the samelead or different leads, if more than one lead is provided. A programmay be defined directly, by selecting parameters and electrodes, or byzone-based programming, in which parameters and electrodes areautomatically determined by the programmer in response to manipulationor positioning of stimulation zones.

Stimulation generator 60 is electrically coupled to electrodes 48A-P viaconductors of the respective lead, such as lead 12 in FIG. 1 or leads 32in FIG. 2, in implementations in which electrodes 48A-P are carried by,located on, leads. Stimulation generator 60 may be electrically coupledto one or more housing (“can”) electrodes 48Q via an electricalconductor disposed within the housing of implantable stimulator 34 ofFIG. 1 or FIG. 2. Housing electrode 48Q may be configured as a regulatedor unregulated electrode to form an electrode configuration inconjunction with one or more of electrodes 48A-48P located on leads ofthe IMD. Housing electrode 48Q may be configured for use as an anode tosource current substantially simultaneously with one or more electrodes,e.g., any of electrodes 48A-48P, on one or more leads configured for useas anodes.

Stimulation generator 60 may include stimulation generation circuitry togenerate stimulation pulses or waveforms and circuitry for switchingstimulation across different electrode combinations, e.g., in responseto control by processor 50. Stimulation generator 60 produces anelectrical stimulation signal in accordance with a program based oncontrol signals from processor 50.

For example, stimulation generator 60 may include a charging circuitthat selectively applies energy from power source 54 to a capacitormodule for generation and delivery of a supply voltage for generation ofstimulation signal. In addition to capacitors, the capacitor module mayinclude switches. In this manner, the capacitor module may beconfigurable, e.g., based on signals from processor 50, to store adesired voltage for delivery of stimulation at a voltage or currentamplitude specified by a program. For delivery of stimulation pulses,switches within the capacitor module may control the widths of thepulses based on signals from processor 50.

In one example implementation, e.g., an omnipolar arrangement,stimulation generator 60 may be configured to deliver stimulation usingone or more of electrodes 48A-P as stimulation electrodes, e.g., anodes,while substantially simultaneously delivering stimulation using housingelectrode 48Q as a stimulation electrode, e.g., anode. The anodes on thelead(s) and the housing may be used to deliver stimulation inconjunction with one or more cathodes on the lead(s). As oneillustration, an electrode combination selected for delivery ofstimulation current may comprise an anode on the IMD housing, and anodeon a lead, and a cathode on the same lead or a different lead. In otherexamples, the electrode combination may include multiple anodes and/ormultiple cathodes on one or more leads in conjunction with at least oneanode on the IMD housing. In some examples, the electrode combinationmay include one or more anodes on one or more leads, and one or morecathodes on the same lead or a different lead, e.g., abipolar/multipolar arrangement. In other examples, the electrodecombination may include an anode on the housing, and one or morecathodes on one or more leads, e.g., omnipolar arrangement. In yetanother example, the electrode combination may include a cathode on thehousing, and one or more additional cathodes on one or more leads, alongwith one or more anodes also on the leads, e.g., a variation of anomnipolar arrangement.

Telemetry circuitry 56 may include a radio frequency (RF) transceiver topermit bi-directional communication between implantable stimulator 34and each of clinician programmer 20 and patient programmer 22. Telemetrycircuitry 56 may include an antenna 57 that may take on a variety offorms. For example, antenna 57 may be formed by a conductive coil orwire embedded in a housing associated with implantable stimulator 34.Alternatively, antenna 57 may be mounted on a circuit board carryingother components of implantable stimulator 34 or take the form of acircuit trace on the circuit board. In this way, telemetry circuitry 56may permit communication with clinician programmer 40 and patientprogrammer 22 in FIG. 1 or external programmer 40 in FIG. 2, to receive,for example, new programs or program groups, or adjustments to programsor program groups.

Power source 54 may be a non-rechargeable primary cell battery or arechargeable battery and may be coupled to power circuitry. However, thedisclosure is not limited to implementations in which the power sourceis a battery. In another example, as an example, power source 54 maycomprise a supercapacitor. In some examples, power source 54 may berechargeable via induction or ultrasonic energy transmission, andinclude an appropriate circuit for recovering transcutaneously receivedenergy. For example, power source 54 may be coupled to a secondary coiland a rectifier circuit for inductive energy transfer. In additionalembodiments, power source 54 may include a small rechargeable circuitand a power generation circuit to produce the operating power.Recharging may be accomplished through proximal inductive interactionbetween an external charger and an inductive charging coil withinstimulator 34. In some embodiments, power requirements may be smallenough to allow stimulator 34 to utilize patient motion at least in partand implement a kinetic energy-scavenging device to trickle charge arechargeable battery. A voltage regulator may generate one or moreregulated voltages using the battery power.

According to the techniques of the disclosure, a clinician implants atleast one lead 32 at an angle relative to and across an anatomicalmidline of spinal cord 38 of patient 36. In some examples, the at leastone lead 32 is implanted at an angle of 5-20 degrees relative to theanatomical midline of spinal cord 38 of patient 36. In some examples ofthe techniques disclosed herein, the clinician implants a first lead 32Aand second lead 32B angled 5-20 degrees relative to and across theanatomical midline of spinal cord 38. In alternate examples, the firstlead 32A is implanted parallel to and offset from the anatomical midlineof spinal cord 38, while the second lead 32B is implanted at an angle of5-20 degrees relative to and across the anatomical midline of spinalcord 38. Such an implantation procedure as described herein may ensurethat at least several electrodes are implanted on either side of thephysiological midline of spinal cord 38.

After surgical implantation of stimulator 34, and outside of theoperating room, the clinician may test various combinations ofelectrodes 48 to determine the combination that provides the greatestpain relief to the patient. For example, in response to commands fromexternal programmer 40, processor 50 may control stimulation generator60 to deliver electrical neurostimulation to patient 36 via a pluralityof combinations of electrodes 48. The clinician may use feedback fromthe patient regarding the plurality of combinations of electrodes 48 toidentify a position of the physiological midline of spinal cord 38. Theclinician selects, based on the location of the physiological midline ofspinal cord 38, at least one electrode of the plurality of electrodesfor subsequent delivery of electrical neurostimulation therapy to thepatient. Processor 50 controls stimulation generator 60 to deliverelectrical neurostimulation to patient 36 according to the selected atleast one electrode of the plurality of electrodes to provide painrelief therapy to patient 36.

FIG. 3 is a functional block diagram illustrating various components ofan external programmer 40 for an implantable stimulator 34. Externalprogrammer 40 of FIG. 3 may be a clinician programmer or a patientprogrammer. External programmer 40 includes processor 53, memory 55,telemetry module 67, user interface 59, and power source 61. In general,processor 53 controls user interface 59, stores and retrieves data toand from memory 55, and controls transmission of data with implantablestimulator 34 through telemetry module 67. Processor 53 may take theform of one or more microprocessors, controllers, DSPs, ASICS, FPGAs, orequivalent discrete or integrated logic circuitry. The functionsattributed to processor 53 herein may be embodied as software, firmware,hardware or any combination thereof.

Memory 55 may store instructions that cause processor 53 to providevarious aspects of the functionality ascribed to external programmer 40herein. Memory 55 may include any fixed or removable magnetic, optical,or electrical media, such as RAM. ROM, CD-ROM, magnetic disks, EEPROM,or the like. Memory 55 may also include a removable memory portion thatmay be used to provide memory updates or increases in memory capacities.A removable memory may also allow patient data to be easily transferredto another computing device, or to be removed before programmer 40 isused to program therapy for another patient. Memory 55 may also storeinformation that controls operation of implantable stimulator 34, suchas therapy delivery values.

In some examples, external programmer 40 includes an image capturingdevice 63. The image capturing device 63 may be built into the externalprogrammer 40 or may be connected to the external programmer 40 via aninterface using a wired or wireless connection. The processor 53 maycontrol the image capturing device 63 to capture images as specified bythe user of the external programmer 40. In some examples, imagecapturing device 63 may be a digital camera or web camera integratedwith or coupled to programmer 40 to capture digital photographs ofimages presented on hardcopy media, such as film or paper, or a digitalimage display screen. Alternatively, the programmer may obtain the imageelectronically from an imaging device, a network storage server, aremovable storage medium such as Flash memory, or other devices,directly or over a network.

A clinician or patient 36 interacts with user interface 59 in order to,for example, manually select, change, or modify programs, e.g., byadjusting voltage or current amplitude, adjusting pulse rate, adjustingpulse width, or selecting different electrode combinations orconfigurations, and may provide efficacy feedback, or view stimulationdata. User interface 59 may include a screen and one or more inputbuttons that allow external programmer 40 to receive input from a user.The screen may be, for example, a liquid crystal display (LCD), plasmadisplay, organic light emitting diode (OLED), electrophoretic displays,dot matrix display, or touch screen. The input buttons may include atouch pad, increase and decrease buttons, emergency shut off button, andother input media needed to control the stimulation therapy.

Using the techniques of this disclosure, a clinician or patient 36 maygraphically define desired stimulation regions using interface 59, andmay capture an image of the stimulated regions and the placement of theleads that stimulate the regions using the image capturing device 63.The clinician or patient 36 may utilize, for example, the user interface59 to control the image capturing device 63 to obtain an image and tomanipulate the image, as will be described in more detail below. In oneexample, the clinician or patient may utilize the image capturing device63 directly to obtain the image.

Telemetry module 67 allows the transfer of data to and from stimulator34. Telemetry module 67 may communicate automatically with stimulator 34at a scheduled time or when the telemetry module detects the proximityof the stimulator. Alternatively, telemetry module 67 may communicatewith stimulator 34 when signaled by a user through user interface 59. Tosupport RF communication, telemetry module 44 may include appropriateelectronic components, such as amplifiers, filters, mixers, encoders,decoders, and the like. In other examples, telemetry module 67 mayemploy other communication standards such as, for example, Bluetooth®and telemetry module 67 may include the appropriate Bluetooth®components.

Programmer 40 may communicate wirelessly with implantable stimulator 34using, for example, RF communication or proximal inductive interactionor other communication standards such as, for example, Bluetooth®. Thiswireless communication is possible through the use of telemetry module67 which may be coupled to an internal antenna or an external antenna.Telemetry module 67 may be similar to telemetry module 57 of implantablestimulator 34.

Programmer 40 may also be configured to communicate with anothercomputing device via wireless communication techniques, or directcommunication through a wired, e.g., network, connection. Examples oflocal wireless communication techniques that may be employed tofacilitate communication between programmer 40 and another computingdevice include RF communication based on the 802.11 or Bluetooth®specification sets, infrared communication, e.g., based on the IrDAstandard.

Power source 61 delivers operating power to the components of programmer40. Power source 61 may be a rechargeable battery, such as a lithium ionor nickel metal hydride battery. Other rechargeable or conventionalbatteries may also be used. In some cases, external programmer 40 may beused when coupled to an alternating current (AC) outlet, i.e., AC linepower, either directly or via an AC/DC adapter. Power source 61 mayinclude circuitry to monitor power remaining within a battery. In thismanner, user interface 59 may provide a current battery level indicatoror low battery level indicator when the battery needs to be replaced orrecharged. In some cases, power source 61 may be capable of estimatingthe remaining time of operation using the current battery.

According to the techniques of the disclosure, a clinician may, viaexternal programmer 40, test various combinations of electrodes 48 ofimplantable stimulator 34 to determine the combination that provides thegreatest pain relief to the patient. For example, the clinician, viauser interface 59 of external programmer 40, may control implantablestimulator 34 to deliver electrical neurostimulation to patient 36 via aplurality of combinations of electrodes 48.

The clinician may use feedback from the patient regarding the pluralityof combinations of electrodes 48 to identify a position of thephysiological midline of spinal cord 38. For example, upon determiningthat patient 36 experiences suppression of a pain sensation and/orparesthesia on only a right lateral side of patient 36, the clinicianmay determine that the electrodes of the electrode combination arelocated to the right of the physiological midline of spinal cord 38.Further, upon determining that patient 36 experiences suppression of apain sensation and/or paresthesia on only a left lateral side of patient36, the clinician may determine that the electrodes of the electrodecombination are located to the left of the physiological midline ofspinal cord 38. By determining that patient 36 experiences suppressionof a pain sensation and/or paresthesia on both a right and a leftlateral side of patient 36, the clinician may determine that at some ofthe electrodes of the electrode combination are located to the left andright of the physiological midline of spinal cord 38, e.g., thephysiological midline of spinal cord 38 lies between the electrodes ofthe electrode combination. The clinician selects, based on the locationof the physiological midline of spinal cord 38, at least one electrodeof the plurality of electrodes for subsequent delivery of electricalneurostimulation therapy to the patient. In some examples, the clinicianselects a combination of electrodes having electrodes positioned to botha left and a right lateral side of the physiological midline.

In some examples, processor 53 determines, based on the delivery of theelectrical neurostimulation, a position of the physiological midline ofspinal cord 38. For example, processor 53 may monitor a physiologicalresponse of a tissue of patient 36 during delivery of a electricalneurostimulation according to a plurality of different electrodecombinations. In some examples, the tissue response is an evokedcompound action potential (eCAP) response of a nerve fiber of patient36. In some examples, the eCAP response arises from an externalstimulation device, such as a transcutaneous electrical nervestimulation (TENS) device, on one side of the patient's body. In someexamples, the external stimulation device is attached to the patient'sleg, buttocks, or one side of the lower back. While the externalstimulation device delivers electrical nerve stimulation, electrodesperforming eCAP monitoring detect the eCAP signal on that side of thebody. In some examples, eCAP monitoring is performed in the operatingroom. In other examples, the tissue response is a visible muscletwitching response of patient 36.

By determining that a first electrode combination evokes a response ononly a right lateral side of patient 36, processor 50 may determine thatthe electrodes of the first electrode combination are located to theright of the physiological midline of spinal cord 38. Further, bydetermining that a second electrode combination evokes a response ononly a left lateral side of patient 36, processor 53 may determine thatthe electrodes of the second electrode combination are located to theleft of the physiological midline of spinal cord 38. By determining thata third electrode combination evokes a response on both a right and aleft lateral side of patient 36, processor 53 may determine that at someof the electrodes of the third electrode combination are located to theleft and right of the physiological midline of spinal cord 38, e.g., thephysiological midline of spinal cord 38 lies between the electrodes ofthe third electrode combination. In some examples, processor 50determines whether a particular electrode combination evokes a responseof patient 36 by increasing the magnitude of the electrical stimulationand determining the motor threshold of patient 36 (e.g., the magnitudeat which patient 36 experiences muscle contractions) on one side of thebody or the other.

Processor 53 selects, based on the location of the physiological midlineof spinal cord 38, at least one electrode of the plurality of electrodesfor subsequent delivery of electrical neurostimulation therapy to thepatient. In some examples, processor 53 selects a combination ofelectrodes having electrodes positioned to both a left and a rightlateral side of the physiological midline (e.g., the third electrodecombination in the above example). Processor 53 controls delivery of theelectrical neurostimulation via the selected combination of electrodesfor pain relief therapy for patient 36.

In some examples, user interface 59 includes a display screen thatprovides an image of spinal cord 38 of patient 36. In such an example,the clinician provides, via user interface 59, an indication of alocation of an anatomical midline of spinal cord 38. Processor 53 storesthe location of the anatomical midline in memory 55. Based on theindication of the location of the anatomical midline, processor 53generates a representation of the anatomical midline of spinal cord 38relative to the image of spinal cord 38 of patient 36 for display to theclinician via user interface 59. Furthermore, as described above,processor 53 determines a location of the physiological midline ofspinal cord 38 or receives, from the clinician, an indication of thelocation of the physiological midline from the clinician, and processor53 stores the location of the physiological midline in memory 55. Insome examples, processor 53 stores the location of the physiologicalmidline within memory 52 of implantable stimulator 34 together withfluoroscopic imagery data for patient 36. Further, based on the locationof the physiological midline of spinal cord 38, processor 53 generates arepresentation of the physiological midline of spinal cord 38 relativeto the image of spinal cord 38 of patient 36 for display to theclinician via user interface 59.

FIGS. 4A-4B are illustrations of example leads for delivering electricalneurostimulation in accordance with the techniques of the disclosure.The examples of FIGS. 4A-4B depict implantable medical leads 32implanted along T6-T7 vertebrae of spine 38 of patient 36. Each of leads32 further includes a plurality of electrodes 48.

In the example of FIG. 4A, a clinician implants leads 32A and 32Bparallel to each other and at an angle relative to and across anatomicalmidline 410 of spinal cord 38 of patient 36. In some examples, theclinician implants leads 32A and 32B at an angle of 5-20 degreesrelative to anatomical midline 410 of spinal cord 38 of patient 36. Suchan implantation procedure as described herein may ensure that at leastsome of the electrodes are implanted on either side of physiologicalmidline 420 of spinal cord 38. For example, an electrode combinationincluding electrodes 48A of lead 32A and 48B of lead 32B are disposed oneither side of physiological midline 420, and therefore may causesuppression of a pain sensation and/or paresthesia on both a left and aright lateral side of patient 36. However, an electrode combinationincluding electrodes 48C of lead 32A and 48D of lead 32B does notinclude electrodes to the left lateral side of physiological midline420. Thus, electrical stimulation via electrodes 48C and 48D may onlycause suppression of a pain sensation and/or paresthesia on a rightlateral side of patient 36. By testing various combinations ofelectrodes 48, the clinician may determine a combination of electrodesthat lies to both a left and a right lateral side of patient 36, andthereby determine the electrode combination that provides the greatestpain relief to the patient.

In the example of FIG. 4B, a clinician implants lead 32A parallel to andoffset from anatomical midline 410 of spinal cord 38 and implants lead32B at an angle of 5-20 degrees relative to anatomical midline 410 ofspinal cord 38 of patient 36. Such an implantation procedure asdescribed herein may ensure that at least several electrodes areimplanted on either side of the physiological midline of spinal cord 38.

For example, an electrode combination including electrodes 48G of lead32A and 48F of lead 32B are disposed on either side of physiologicalmidline 420, and therefore may cause suppression of a pain sensationand/or paresthesia on both a left and a right lateral side of patient36. However, an electrode combination including electrodes 48E of lead32A and 48H of lead 32B does not include electrodes to the left lateralside of physiological midline 420. Thus, electrical stimulation viaelectrodes 48E and 48H may only cause suppression of a pain sensationand/or paresthesia on a right lateral side of patient 36. By testingvarious combinations of electrodes 48, the clinician may determine acombination of electrodes that lies to both a left and a right lateralside of patient 36, and thereby determine the electrode combination thatprovides the greatest pain relief to the patient.

FIGS. 5A-5D illustrate an exemplary screen shot 500 of a display on userinterface 59 of programmer 40, in accordance with the techniques of thedisclosure. In one example, programmer 40 may be a clinician programmer.FIGS. 5A-5D are discussed in the context of a patient receiving spinalcord stimulation therapy as an illustrative example. A programmer, e.g.,programmer 40, may receive user input via the user interface 59 to setup leads and parameters that define one or more stimulation programs fordelivering therapy to a patient. A stimulation program may be deliveredby an implantable stimulator individually or in combination with otherprograms, e.g., on a time-interleaved basis. A program may define anelectrode combination, including a selected set of electrodes fordelivery of stimulation and polarities of such electrodes, pulse currentor pulse voltage amplitudes delivered by respective electrodes, pulsewidth and pulse rate. The user may set up a profile for the session andthe patient, and proceed to configure placement of the leads.

To provide an accurate representation of implanted leads for spinal cordstimulation, the user may select which leads will be programmed withtherapy. In this example, there are up to 2 leads from which a user mayselect. However, in other examples there may be more or less leadsavailable to the user from which to select. FIG. 5A illustrates a leadset up screen where the user is prompted to indicate whether all theleads, for the given number of leads implanted or being trialed, will beplaced in the same region and/or programmed together by indicating “Yes”or “No.” The user may assign implanted leads to one or more regions,where the regions represent the anatomical implant location of the leadsassociated with the regions. A lead region may be, for example, suchentity as “lumbar spine” or “epidural thoracic.” In one example, wheredifferent leads are selected for different regions, the user may viewand/or program each region where only the leads associated with aselected region are viewed and/or programmed. In one example, the usermay assign the case electrodes to one or more regions, either alone orin combination with the implanted leads.

Upon selecting the leads, a representation of the leads to be programmedfor that region may be shown on the screen. Referring to FIG. 5A, thegraphical representation of two leads 32, each with 8 electrodes may beshown on the screen, because the user selected to program them alltogether (in this example two leads). The user may be presented with anoption to import an image for the lead region being programmed. Theimage may be for example a fluoroscopic image of the region in whichtherapy is to be applied. A button 611 labeled “Import Fluoro Image”appears on the display as shown in FIG. 5A, which the user may select ifthe user opts to import a fluoroscopic image of the leads assigned tothe region for which therapy is being programmed. In another example,the display may also have a “Start Camera” button (not shown), whichmay, upon selection by the user, display an image acquired by thecamera, which the user may select to use as the background image, as analternative for importing a previously-acquired image. Therefore, a usermay have an option to either use a camera or import apreviously-acquired image. One or more examples of acquiring and storinga fluoroscopic image of a therapy region in a patient may be describedin U.S. Pat. No. 8,744,591 to Davis et al., titled “STORING IMAGE OFTHERAPY REGION IN IMPLANTABLE MEDICAL DEVICE,” issued on Jun. 3, 2014and in U.S. patent application Ser. No. 14/085,573 to Davis et al.,titled “ASSIGNMENT AND MANIPULATION OF IMPLANTABLE LEADS IN DIFFERENTANATOMICAL REGIONS WITH IMAGE BACKGROUND” and filed on Nov. 20, 2013,the entire content of each of which is incorporated herein by reference.

The display screen may also present options to the user to manipulatethe positions or the representation of the leads 32. In the example ofFIG. 5A, the user may move a lead 32 by tapping and holding on the lead32 and dragging it, or the user may rotate or curve a lead 32 by tappingand holding on an anchor point and dragging as indicated by instructionsprovided to the user on the screen. The user may also swap theorientation of leads 32 by selecting the corresponding function button.The user may also manipulate the leads 32 further by bending, resizing,and shaping the graphical representation of the leads or portions of theleads to achieve a better match between the graphical leads and theimage of the leads in the anatomical background image. In one example,the user may select starting and ending points of the leads 32 in theimage (e.g., to match distal and proximal electrode locations in theimage), and the programmer may automatically draw the graphicalrepresentation of the leads 32 between the two points. The display mayalso show the electrode configuration, showing how the leads 32 areinserted. In one example, an option may be displayed to “Check LeadInsertion” to check that the leads are inserted correctly. The displaymay also present the user with the ability to manipulate thefluoroscopic image, as shown on the left side of the screen. However,the fluoroscopic image tools may not be highlighted until a fluoroscopicimage is imported.

In some examples, upon importing a fluoroscopic image of spinal cord 38,the representation of the leads 32 may be superimposed on thefluoroscopic image of spinal cord 38. While it is not shown, a similarscreen may be displayed for each of the regions when multiple regionsare defined, and the user may import a fluoroscopic image to one or moreregions, by clicking on a tab for the region and clicking on the “ImportFluoro Image” for that region.

In one example, the user interface may display the image and graphicalrepresentation of leads in 2D. In this example, the user interface maydisplay the same region and the corresponding graphical representationof leads implanted in the region in 2D from different perspectivescorresponding to different angles or cross sections, as the implantedleads may curve in more than one direction spatially, and allow the userto manipulate the graphical representation of leads for eachperspective. In another example, the user interface may display theimage and graphical representation of leads in 3D. In this example, theuser interface may display the region and the corresponding graphicalrepresentation of leads implanted in the region in 3D, and may allow theuser to rotate and manipulate the image and the graphical representationin all directions.

After the leads and fluoroscopic image have been manipulated to matchfor a given region, the process may be repeated for all lead regions (ifmultiple regions are programmed). The fluoroscopic image may becompressed and stored in the device, by selecting the button labeled“Program” on the screen. Selecting “program” may program all the changesto the device. The display may also present the user with other optionslike “Tools” and “Summary” in addition to “Programming.” Subsequently,the creation of therapy may occur (per lead region) on the final leadrepresentation of the leads with the fluoroscopic image as background.

Each process described for the example of assigning all the leads to oneimage, may be used with each of the different regions. When multipleregions are defined, multiple fluoroscopic images may be linked tocorresponding multiple lead electrode images and locations, andattributes related to the leads and the images may be linked thereto,and the combination of the images, leads, and attributes may beprogrammed and stored on medical devices, such as implantable stimulator34 of FIG. 1. Each of the images may be associated with an anatomicalregion, or with different perspectives of the same region, for example.Additionally, a lead 32 may be programmed to provide therapy associatedwith more than one region. In one example, the user may assign andprogram the case electrodes for certain anatomical regions in the samemanner the user assigns and programs implanted leads.

According to the techniques of the disclosure, the clinician may useuser interface 500 to mark, in reference to the first and second leads32, the location of the anatomical midline 410 of spinal cord 38 via afluoroscope. As depicted in FIG. 5A, the clinician selects, via cursor510, button 502 to set an anatomical midline of spinal cord 38 ofpatient 34. In the example of FIG. 5B, the clinician sets a position forthe anatomical midline by using cursor 510 to drag a line 410representing the anatomical midline of the spinal cord 38 over afluoroscopic image of spinal cord 38. In some examples, upon setting aposition of the anatomical midline of the spinal cord 38, the clinicianmay determine the location of the physiological midline of spinal cord38 via patient feedback, and mark the location of the physiologicalmidline of spinal cord 38 on user interface 500 in a similar fashion tothat of the anatomical midline 410.

In further examples, as illustrated in FIG. 5C, user interface 500includes a button 504 to determine the physiological midline of spinalcord 38. Upon setting a position of the anatomical midline of the spinalcord 38, the clinician may select button 504 via cursor 510. In responseto the clinician selecting button 504, processor 53 of externalprogrammer 40 determines a position of the physiological midline ofspinal cord 38. As described above, processor 50 may monitor aphysiological response of a tissue of patient 36 during delivery ofelectrical neurostimulation according to a plurality of differentelectrode combinations. In some examples, the tissue response is anevoked compound action potential (eCAP) response of a nerve fiber ofpatient 36. In some examples, the tissue response is a visible muscletwitching response of patient 36. For example, by determining that oneor more electrode combinations evoke a response on only a right lateralside of patient 36, processor 50 may determine that the one or moreelectrode combinations are located to the right of the physiologicalmidline of spinal cord 38. Further, by determining that one or moreelectrode combinations evoke a response on only a left lateral side ofpatient 36, processor 50 may determine that the one or more electrodecombinations are located to the left of the physiological midline ofspinal cord 38. By determining that one or more electrode combinationsevoke a response on both a right and a left lateral side of patient 36,processor 50 may determine that at least some of the electrodes of theone or more electrode combinations are located both to the left andright of the physiological midline of spinal cord 38, e.g., thephysiological midline of spinal cord 38 lies between the electrodes ofthe one or more electrode combinations. Accordingly, based on thephysiological response of the tissue during delivery of electricalneurostimulation according to the plurality of different electrodecombinations, processor 50 determines the position of the physiologicalmidline 420. As depicted in FIG. 5D, processor 50 marks on user display500 the position of physiological midline 420.

FIG. 6 is a conceptual diagram illustrating a stimulation zone ofelectrical stimulation therapy. As described above, system 30 deliverselectrical neurostimulation according to a plurality of differentcombinations of electrodes 48. By monitoring a physiological response ofa tissue of patient 36 during delivery of the electricalneurostimulation according to the plurality of different electrodecombinations, system 30 may determine a position of a physiologicalmidline 420 of spinal cord 38 of patient 36.

As depicted in FIG. 6, once the location of the physiological midline420 of spinal cord 38, the clinician, via programmer 40, selects acombination of electrodes that includes one or more electrodes to a leftlateral side of the determined physiological midline 420 and a rightlateral side of physiological midline 420. For example, as depicted inFIG. 6, the clinician selects one or more electrodes that results inelectrical field 116 that lies to a left lateral side of physiologicalmidline 420 and a right lateral side of physiological midline 420.Implantable stimulator 34 uses electrodes 48B, 49F, and 48G to deliverelectrical stimulation to a target tissue site 118 of patient 36. Thecentroid of electrical field 116 is indicated by icon 112.

In some examples, programmer 40 receives, from the clinician via userinterface 59, a selection of one or more electrode combinations. Inother examples, processor 53 of programmer 40 automatically determines aselection of one or more electrode combinations based on the detectedlocation of physiological midline 420. In some examples, programmer 40may automatically balance the anodes and cathodes of an electrodecombination such that, after balancing, implantable stimulator 34 usesthe same number of anodes and cathodes to deliver electrical stimulationto target tissue site 118. In other examples, programmer 40 selects anelectrode combination that has differing numbers of anodes and cathodes.In yet other examples, programmer 40 selects an electrode combinationthat has a single anode and multiple cathodes. In yet other examples,programmer 40 selects an electrode combination that has multiple anodesand a single cathode. Additional techniques for selecting combinationsof electrodes are provided in U.S. Pat. No. 8,560,080 to Goetz, issuedon Oct. 15, 2013, the entire content of which is incorporated herein byreference.

Thus, by determining the location of the physiological midline 420, thesystem of the present disclosure may more accurately select an electrodecombination for delivery of stimulation to patient 36. For example, bydetermining the location of the physiological midline, the system mayselect an electrode combination that includes one or more electrodes toa left lateral side of the determined physiological midline 420 and aright lateral side of physiological midline 420. By selecting such anelectrode combination, the system of the present disclosure may createan electrical field 116 that stimulates tissue on both left lateral sideand a right lateral side of patient 36. Alternatively, the system mayselect an electrode combination that includes one or more electrodesonly to a left lateral side of the determined physiological midline 420or only to a right lateral side of physiological midline 420. Byselecting such an electrode combination, the system of the presentdisclosure may create an electrical field 116 that stimulates tissue ononly a left lateral side or only a right lateral side of patient 36,respectively. Such a system may allow for increased reliability andefficacy in lead placement during surgery. Accordingly, a system asdescribed herein may eliminate the need to perform testing of theimplanted electrodes within the operation room, which may reduce thecost of the procedure, increase the reliability of the feedback receivedfrom the patient, and eliminate the need to wake the patient up fromanesthesia to provide feedback on the electrical neurostimulationtherapy, paresthesia, and pain sensations.

FIG. 7 is a flowchart depicting an example operation according to thetechniques of the disclosure. For convenience, FIG. 7 is described withrespect to FIG. 1. According to the techniques of the disclosure, aclinician implants at least one lead 32 at an angle relative to andacross an anatomical midline of spinal cord 38 of patient 36 (700). Insome examples, the at least one lead 32 is implanted at an angle of 5-20degrees relative to the anatomical midline of spinal cord 38 of patient36. In some examples of the techniques disclosed herein, the clinicianimplants a first lead 32A and second lead 32B angled 5-20 degreesrelative to and across the anatomical midline of spinal cord 38. Inalternate examples, the first lead 32A is implanted parallel to andoffset from the physiological midline of spinal cord 38, while thesecond lead 32B is implanted at an angle of 5-20 degrees relative to andacross the physiological midline of spinal cord 38. Such an implantationprocedure as described herein may ensure that at least severalelectrodes are implanted on either side of the physiological midline ofspinal cord 38.

After implanting the lead, the clinician, via external programmer 40,controls delivery of electrical stimulation according to a plurality ofcombinations of electrodes 48 (702). The clinician determines a locationof a physiological midline of the patient 36 based on the delivery ofelectrical stimulation according to a plurality of combinations ofelectrodes 48 (704). In some examples, the clinician uses feedback fromthe patient regarding the different combinations of electrodes toidentify a position of the physiological midline of spinal cord 38. Inother examples, programmer 40 determines the location of a physiologicalmidline based upon a tissue response of patient 36 to the electricalstimulation in the manner described above. The clinician may use a userinterface to mark, in reference to the first and second leads, thelocation of the anatomical midline of spinal cord 38 via a fluoroscope,and to further mark the location of the physiological midline of spinalcord 38 via the patient feedback. Based on the location of thephysiological midline of spinal cord 38, the clinician selects at leastone electrode for subsequent delivery of electrical stimulation (706).Implantable stimulator 34 delivers electrical stimulation to patient 36via the selected at least one electrode to provide pain relief therapyto patient 36 (708).

The techniques described in this disclosure may be implemented, at leastin part, in hardware, software, firmware or any combination thereof. Forexample, various aspects of the described techniques may be implementedwithin one or more processors, including one or more microprocessors,digital signal processors (DSPs), application specific integratedcircuits (ASICs), field programmable gate arrays (FPGAs), or any otherequivalent integrated or discrete logic circuitry, as well as anycombinations of such components. The term “processor” or “processingcircuitry” may generally refer to any of the foregoing logic circuitry,alone or in combination with other logic circuitry, or any otherequivalent circuitry. A control unit comprising hardware may alsoperform one or more of the techniques of this disclosure.

Such hardware, software, and firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. In addition, any of thedescribed units, modules or components may be implemented together orseparately as discrete but interoperable logic devices. Depiction ofdifferent features as modules or units is intended to highlightdifferent functional aspects and does not necessarily imply that suchmodules or units must be realized by separate hardware or softwarecomponents. Rather, functionality associated with one or more modules orunits may be performed by separate hardware or software components, orintegrated within common or separate hardware or software components.

The techniques described in this disclosure may also be embodied orencoded in a computer-readable medium, such as a computer-readablestorage medium, containing instructions. Instructions embedded orencoded in a computer-readable storage medium may cause a programmableprocessor, or other processor, to perform the method, e.g., when theinstructions are executed. Computer readable storage media may includerandom access memory (RAM), read only memory (ROM), programmable readonly memory (PROM), erasable programmable read only memory (EPROM),electronically erasable programmable read only memory (EEPROM), flashmemory, a hard disk, a CD-ROM, a floppy disk, a cassette, magneticmedia, optical media, or other computer readable media.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method comprising: controlling, by one or moreprocessors, an electrical neurostimulation therapy device to deliverelectrical neurostimulation therapy to a patient via a plurality ofcombinations of a plurality of electrodes disposed on a first lead and asecond lead connected to the electrical neurostimulation therapy device,wherein the first lead is positioned across an anatomical midline of aspinal cord of a patient and angled relative to the anatomical midlineof the spinal cord so that at least one electrode of the plurality ofelectrodes disposed on the first lead is positioned to a left lateralside of the anatomical midline of the spinal cord and at least one otherelectrode of the plurality of electrodes disposed on the first lead ispositioned to a right lateral side of the anatomical midline of thespinal cord, and wherein the second lead is positioned parallel to thespinal cord of the patient; determining, by the one or more processorsand for multiple combinations of the plurality of combinations of theplurality of electrodes, a therapeutic effect of the electricalneurostimulation therapy on the patient; and determining, by the one ormore processors and based on the therapeutic effects on the patient ofthe multiple combinations of the plurality of combinations of theplurality of electrodes, a location of a physiological midline of thespinal cord of the patient relative to the multiple combinations of theplurality of combinations of the plurality of electrodes.
 2. The methodof claim 1, further comprising: selecting, by the one or more processorsand based on the location of the physiological midline relative to themultiple combinations of the plurality of combinations of the pluralityof electrodes, one or more electrodes of the plurality of electrodes fordelivery of subsequent electrical neurostimulation therapy to thepatient; and controlling, by the one or more processors, the electricalneurostimulation therapy device to deliver electrical neurostimulationtherapy to the patient via the selected one or more electrodes of theplurality of electrodes.
 3. The method of claim 2, wherein selecting,based on the location of the physiological midline relative to themultiple combinations of the plurality of combinations of the pluralityof electrodes, one or more electrodes of the plurality of electrodes fordelivery of subsequent electrical neurostimulation therapy to thepatient comprises: selecting one or more first electrodes of theplurality of electrodes located to a left lateral side of thephysiological midline; and selecting one or more second electrodes ofthe plurality of electrodes located to a right lateral side of thephysiological midline, and wherein controlling the electricalneurostimulation therapy device to deliver electrical neurostimulationtherapy to the patient via the selected one or more electrodes of theplurality of electrodes comprises controlling the electricalneurostimulation therapy device to deliver electrical neurostimulationtherapy to the patient via the one or more first electrodes and the oneor more second electrodes.
 4. The method of claim 1, wherein determiningthe therapeutic effect of the electrical neurostimulation therapy on thepatient comprises determining that the electrical neurostimulationtherapy on the patient causes one of: a paresthesia sensation in both aleft lateral side and a right lateral side of the patient; a paresthesiasensation in the left lateral side and not the right lateral side of thepatient; a paresthesia sensation in the right lateral side and not theright lateral side of the patient; or no paresthesia sensation in eitherthe left lateral side or the right lateral side of the patient.
 5. Themethod of claim 1, wherein determining the therapeutic effect of theelectrical neurostimulation therapy on the patient comprises determiningthat the electrical neurostimulation therapy on the patient causes oneof: a suppression of a pain sensation in both a left lateral side and aright lateral side of the patient; a suppression of a pain sensation inthe left lateral side and not the right lateral side of the patient; asuppression of a pain sensation in the right lateral side and not theright lateral side of the patient; or no suppression of a pain sensationin either the left lateral side or the right lateral side of thepatient.
 6. The method of claim 1, wherein determining the therapeuticeffect of the electrical neurostimulation therapy on the patientcomprises determining a response of a tissue of the patient to theelectrical neurostimulation therapy.
 7. The method of claim 1, whereindetermining, for the multiple combinations of the plurality ofcombinations of the plurality of electrodes, the therapeutic effect ofthe electrical neurostimulation therapy comprises: determining thatelectrical neurostimulation therapy delivered with a first combinationof the plurality of combinations of the plurality of electrodes causes afirst therapeutic effect in the left lateral side and not the rightlateral side of the patient; and determining that electricalneurostimulation therapy delivered with a second combination of theplurality of combinations of the plurality of electrodes causes a secondtherapeutic effect in the right lateral side and not the left lateralside of the patient, and wherein determining, based on the therapeuticeffects on the patient of the multiple combinations of the plurality ofcombinations of the plurality of electrodes, the location of thephysiological midline of the spinal cord of the patient relative to themultiple combinations of the plurality of combinations of the pluralityof electrodes comprises determining, based on the first and secondtherapeutic effects, that the physiological midline of the spinal cordof the patient is located between the first combination of the pluralityof combinations of the plurality of electrodes and the secondcombination of the plurality of combinations of the plurality ofelectrodes.
 8. The method of claim 1, wherein the second lead ispositioned substantially inferior to the first lead so that the firstlead and second lead at least partially do not overlap along alongitudinal axis of the patient.
 9. A system comprising: a first leadpositioned across an anatomical midline of a spinal cord of a patientand angled relative to the anatomical midline of the spinal cord so thatat least one electrode of a first plurality of electrodes disposed onthe first lead is positioned to a left lateral side of the anatomicalmidline of the spinal cord and at least one other electrode of the firstplurality of electrodes is positioned to a right lateral side of theanatomical midline of the spinal cord, wherein the first lead isconnected to an electrical neurostimulation therapy device; a secondlead positioned parallel to the spinal cord of the patient, the secondlead having a second plurality of electrodes, and wherein the secondlead is connected to the electrical neurostimulation therapy device; theelectrical neurostimulation therapy device, wherein the electricalneurostimulation therapy device is configured to deliver electricalneurostimulation therapy to the patient via a plurality of combinationsof the first plurality of electrodes and the second plurality ofelectrodes; and one or more processors configured to: control theelectrical neurostimulation therapy device to deliver electricalneurostimulation therapy to the patient via the plurality ofcombinations of the first plurality of electrodes and the secondplurality of electrodes: determine, for multiple combinations of theplurality of combinations of the first plurality of electrodes and thesecond plurality of electrodes, a therapeutic effect of the electricalneurostimulation therapy on the patient; and determine, based on thetherapeutic effects on the patient of the multiple combinations of theplurality of combinations of the first plurality of electrodes and thesecond plurality of electrodes, a location of a physiological midline ofthe spinal cord of the patient relative to the multiple combinations ofthe plurality of combinations of the first plurality of electrodes andthe second plurality of electrodes.
 10. The system of claim 9, whereinthe one or more processors are further configured to: select, based onthe location of the physiological midline relative to the multiplecombinations of the plurality of combinations of the first plurality ofelectrodes and the second plurality of electrodes, one or moreelectrodes of the first plurality of electrodes and the second pluralityof electrodes for delivery of subsequent electrical neurostimulationtherapy to the patient; and control the electrical neurostimulationtherapy device to deliver electrical neurostimulation therapy to thepatient via the selected one or more electrodes of the first pluralityof electrodes and the second plurality of electrodes.
 11. The system ofclaim 10, wherein to select, based on the location of the physiologicalmidline relative to the multiple combinations of the plurality ofcombinations of the first plurality of electrodes and the secondplurality of electrodes, one or more electrodes of the first pluralityof electrodes and the second plurality of electrodes for delivery ofsubsequent electrical neurostimulation therapy to the patient, the oneor more processors are further configured to: select one or more firstelectrodes of the first plurality of electrodes and the second pluralityof electrodes located to a left lateral side of the physiologicalmidline; and select one or more second electrodes of the first pluralityof electrodes and the second plurality of electrodes located to a rightlateral side of the physiological midline, and wherein to control theelectrical neurostimulation therapy device to deliver electricalneurostimulation therapy to the patient via the selected one or moreelectrodes of the fist plurality of electrodes and the second pluralityof electrodes, the one or more processors are further configured tocontrol the electrical neurostimulation therapy device to deliverelectrical neurostimulation therapy to the patient via the one or morefirst electrodes and the one or more second electrodes.
 12. The systemof claim 9, wherein to determine the therapeutic effect of theelectrical neurostimulation therapy on the patient, the one or moreprocessors are configured to determine that the electricalneurostimulation therapy on the patient causes one of: a paresthesiasensation in both a left lateral side and a right lateral side of thepatient; a paresthesia sensation in the left lateral side and not theright lateral side of the patient; a paresthesia sensation in the rightlateral side and not the right lateral side of the patient; or noparesthesia sensation in either the left lateral side or the rightlateral side of the patient.
 13. The system of claim 9, wherein todetermine the therapeutic effect of the electrical neurostimulationtherapy on the patient, the one or more processors are configured todetermine that the electrical neurostimulation therapy on the patientcauses one of: a suppression of a pain sensation in both a left lateralside and a right lateral side of the patient; a suppression of a painsensation in the left lateral side and not the right lateral side of thepatient; a suppression of a pain sensation in the right lateral side andnot the right lateral side of the patient; or no suppression of a painsensation in either the left lateral side or the right lateral side ofthe patient.
 14. The system of claim 9, wherein to determine thetherapeutic effect of the electrical neurostimulation therapy on thepatient, the one or more processors are configured to determine aresponse of a tissue of the patient to the electrical neurostimulationtherapy.
 15. The system of claim 9, wherein to determine, for themultiple combinations of the plurality of combinations of the firstplurality of electrodes and the second plurality of electrodes, thetherapeutic effect of the electrical neurostimulation therapy, the oneor more processors are configured to: determine that electricalneurostimulation therapy delivered with a first combination of theplurality of combinations of the first plurality of electrodes and thesecond plurality of electrodes causes a first therapeutic effect in theleft lateral side and not the right lateral side of the patient; anddetermine that electrical neurostimulation therapy delivered with asecond combination of the plurality of combinations of the s pluralityof electrodes and the second plurality of electrodes causes a secondtherapeutic effect in the right lateral side and not the left lateralside of the patient, and wherein to determine, based on the therapeuticeffects on the patient of the multiple combinations of the plurality ofcombinations of the first plurality of electrodes and the secondplurality of electrodes, the location of the physiological midline ofthe spinal cord of the patient relative to the multiple combinations ofthe plurality of combinations of the first plurality of electrodes andthe second plurality of electrodes, the one or more processors areconfigured to determine, based on the first and second therapeuticeffects, that the physiological midline of the spinal cord of thepatient is located between the first combination of the plurality ofcombinations of the first plurality of electrodes and the secondplurality of electrodes and the second combination of the plurality ofcombinations of the first plurality of electrodes and the secondplurality of electrodes.
 16. A method comprising delivering, with anelectrical neurostimulation therapy device, electrical neurostimulationtherapy to the patient via a plurality of combinations of a firstplurality of electrodes disposed on a first lead connected to theelectrical neurostimulation therapy device and a second plurality ofelectrodes disposed along a second lead connected to the electricalneurostimulation therapy device, wherein the first lead is positionedacross an anatomical midline of a spinal cord of a patient and angledrelative to the anatomical midline of the spinal cord so that at leastone electrode of the first plurality of electrodes disposed on the firstlead is positioned to a left lateral side of the anatomical midline ofthe spinal cord and at least one other electrode of the first pluralityof electrodes is positioned to a right lateral side of the anatomicalmidline of the spinal cord, and wherein the second lead is positionedparallel to the anatomical midline of the spinal cord of the patient andwherein the second lead is positioned substantially inferior to thefirst lead so that the first lead and second lead at least partially donot overlap along a longitudinal axis of the patient.